The present invention relates to an automatic circumferential welding apparatus for welding together cylindrical objects while moving along the circumference of the abutted ends of the objects employing an arc welding technique using a consumable electrode. More particularly, the invention relates to an automatic circumferential welding apparatus capable of being taught instructions concerning welding lines associated with plural welding directions and individual points at which the generation of an electric arc should be started and stopped.
In the case of MIG welding applied, for instance, to butt welding around the circumferences of pipes, although no problem is posed when the welding torch is moved upward, a drippy molten pool causes difficulties when the welding torch is moved downward. Consequently, it is common to employ an upward movement split welding technique whereby the torch is always moved upwardly for welding, that is, in clockwise and counterclockwise directions in half circles.
FIG. 1 is a schematic side view illustrating the positional relation between a welding torch and a groove in terms of their relative positions when the edges of abutted pipes are being welded together using a conventional circumferential welding apparatus. In FIG. 1, there are shown pipes 1 to be welded, a groove 2, a welding head 3, a welding torch 4 attached to the welding head 3, a wire reel 5 attached to the welding head 3, and a guide rail 6. A rail 6 is fixed to one of the pipes 1, and the welding head 3, driven by a driving motor, is guided along the rail 6 around the circumference of the pipe 1 in the direction perpendicular to the longitudinal, central axis of the pipe 1. For purposes of the present discussion, the direction of upward movement in FIG. 1 is defined as the X direction. As the welding head 3 moves in the X direction, the welding torch 4 is moved in the X direction. The welding torch 4 is also moved in the Y direction, herein defined as the direction perpendicular to the groove 2, and in the Z direction, that is, the direction perpendicular to the X and Y directions. Thus, the movement of the welding torch 4 is controlled in the X, Y and Z directions so that welding can be carried out by moving the welding torch 4 along the groove, that is, along the welding line.
Due to the fact that it is difficult to arrange the guide rail 6 completely parallel to the groove 2 and perpendicular to the central axis of the pipe 1, it is often necessary to manually adjust the position of the torch 4, particularly, the position in the Y direction, while observing the welding arc. In other words, there is a disadvantage in the welding method described above in that, because much care must be exerted in controlling the positions of the welding torch and the welding line, welding operations performed therewith are generally inefficient.